The influence of catalyst pore structure on catalytic reactions

In the production of chemical industry, the reactant molecules participating in catalytic reactions need to be dispersed through the pores to reach the interior of the catalyst, so the pore structure will be affected by internal diffusion to varying degrees. The diffusion of reactant molecules within catalyst pores includes bulk diffusion, microporous diffusion, configuration diffusion, and surface diffusion. In a small diffusion process, under certain conditions, only one type of diffusion may occur, or several types may occur simultaneously. In other words, the difference in diameter size can lead to changes in the diffusion form and diffusion rate, resulting in varying numbers of particles entering the pores, thereby affecting the reversal rate. 

        The so-called bulk diffusion or volume diffusion refers to the diffusion when the average diameter of molecules (A) is smaller than the pore diameter (d). At this time, the probability of molecules entering the pore and colliding with each other is greater than the probability of colliding with the pore wall. The resistance mainly comes from collisions between molecules. For systems with high gas pressure, bulk diffusion mainly plays a role. Describe the diffusion rate using FMk's first law.